Big snowfall reversed earlier dry conditions
After a bleak outlook for the mountain snowpack six weeks ago, the water supply specialist with the state’s Snow Survey Office celebrated what he called “awesome April,” when most of the winter’s missing snow accumulated in just a month.
Snowpack increased across the state, “nudging out April 2011 for the king of comebacks,” Water Supply Specialist Scott Pattee said in his monthly recap for the Natural Resources Conservation Service, which maintains 70 mountain SNOTEL sites around the state. The snowpack, or snow-water content, is what counts when it comes to spring runoff.
There have been only two other Aprils since 2009 where there was enough snowfall — and cold enough temperatures — to help the snowpack recover. April snowfall is typically light and followed by warm weather, meaning it evaporates without adding to the overall snowpack and subsequent runoff. But this year, below-normal temperatures slowed stream runoff to levels considerably below normal, Pattee said.
The cool, wet April weather reversed the warm, dry trend that had persisted from January through March, when there were only three or four periods with weather cold enough for snow. In fact, before the shift, snowmelt was well underway in early April and temperatures above freezing had caused the snowpack to peak one to three weeks early, Pattee said.
But it snowed almost every day in April, increasing the snowpack at Harts Pass from 49 inches on April 1, to a peak of 57.4 inches on May 4. That’s more than a week later than the normal peak of April 25, according to the SNOTEL data.
The snow-water equivalent at Harts Pass as of May 15 was 152% of normal, at 54.4 inches, compared to 36 inches in a normal year. In fact, the Harts Pass snowpack has increased by about an inch over the past week, Pattee said.
The April snowfall increased the statewide snowpack to 114% of normal, with the Upper Columbia River basin at 107% of the 30-year median.
As of May, the Methow snowpack was 128% of median; last May, it was 119%. The Upper Columbia snowpack was 118% of average in April, and 104% of average for the water year, which starts in October.
April streamflows for the Methow River at Pateros were just 67% of average, since snow hasn’t been melting at the higher elevations, Pattee said.
Heat, drought forecast
Despite the generous snowpack, temperatures for this area through July are likely to be above normal, with expectations of less precipitation than normal, according to the U.S. Drought Monitor.
The dividing line between not being in drought and being rated as “abnormally dry” goes through western Okanogan County, according to the Drought Monitor. The upper Methow Valley is not currently in drought, although the lower valley is in the “abnormally dry” zone, with “moderate drought” further east.
“Abnormally dry” and “moderate drought” are the two least-severe categories used by the drought monitor, which includes three more serious ratings above that, from “severe drought” to “exceptional drought.”
